Same here, she told me she cheated on all 6 or 7 of her boyfriends before we started dating and I still went for it. All my friends at the time did not like her and told me not too, so of course I just stopped hanging out with them and hung out with her more. One of those friends hooked up with her months before we started dating when they were both trashed, and she said it was not consensual because she was too drunk, they both were very drunk. I am 99% sure it was consensual as she had made comments about him and was extra flirty towards him (and initiated it too - I was with them early on in the night). She didn't want me to hang out with him anymore.
We dated off and on through all of college and then some. She even got me to agree an open relationship (almost two years into the relationship) when I had been vocal about how against it I was. Not wanting to lose her at the time, I agreed to the occasional one night stand (to which I told her I probably wouldn't sleep around and never did ). Definitely my mistake here but I was relatively young and naive, and it was my first girlfriend.
She basically hid a full on second relationship with another guy (who also had a girlfriend). She would ditch me constantly on weekends for almost 6 months straight and I had my suspicions but tried to brush them off. When I finally found out, she faked an apology but, as she always did, somehow turned it on me and had me feeling bad by the end. She wasn't the smartest but damn did she know how to manipulate. Every argument had me apologizing somehow even if it was very clear I was right.
Some extra, fun red flags I missed.
At times, her friends hinted or even to some degree straight up told me to move on and run after she did something shitty to me. I never took it seriously. Looking back, it's pretty clear they knew some secrets that I never found out about and were trying to warn me.
My best friend despised her. Saw right through her and warned me throughout the whole thing, he knew the first night he met her something was not right. He still gives me (deserved) crap for it.
She called me drunk a month after we started dating during winter break telling me how I should be proud that she almost tried to kiss another guy but didn't. I was a wreck that break thinking she was cheating on me. But hey, she totally didn't kiss that guy maybe!
Right before we started dating, we got into a small argument and made it very clear she was going to go hook up with another guy that same night and walked out. In a shocking turn of events, she hooked up with another guy. Apparently I wasn't giving her enough attention that night and I just wanted to play ping pong with my friends.
Almost all her friends were guys and she said just didn't get along with other girls. She was very flirtatious by nature and fed into her guy friends a lot, and when I asked why she did, she said she didn't notice or didn't want to hurt their feelings. She definitely noticed and liked the attention. I know having all guy friends isn't always a red flag but in this case it definitely was. She would show me suggestive texts guys sent her and she would respond neutrally, not shutting them down and letting the conversation continue. She said they were so creepy but continued to entertain them and hang out.
My favorite was after we stopped dating, an event between mutual friends brought us back together after I swore her off, and she brought her new guy (I found out about him through a mutual friends snapchat, this was a within a week of her getting me to tell her I loved her again - in person, nonetheless. I'm an idiot.). Queue later in the night, she flirts with me and ditches the guy who she was dating (did I mention I'm an idiot? In my weak defense, she said they were not actually dating, just seeing each other and not exclusive. I believed her as they had met relatively recently. Not my finest moment, part of me knew it was hypocritical of me but I was lost in the moment). He ended up calling her on the way back to her apartment asking where she was and if she was with me. She lied through her teeth saying she was alone and didn't feel well, I tried to yell something in the phone to him and she hung up. I want to believe he heard me, they broke up a few days later.
We did the deed, she called his name out in bed, I threw a used condom at her and went back to the bar. Havent seen her in over 3 years.
She knew I blocked her number so she called me from her dad's cellphone to try and come over during new years later that year like nothing ever happened. I was still having a tough time getting over her but I held strong and it all got better from there, much faster than I thought. Once I thought about it and how terrible the relationship was, everything made so much more sense and it was much easier to move on. So many textbook red flags, reminds me of that bojack horseman quote.
What a waste of my college years. I did learn a lot though so not all was lost. There's probably much more I can't think of and way more I don't even know about, but I'd rather be in the dark at this point as I moved on years ago.